This invention relates to compositions for obtaining regenerated cellulose articles, particularly fibres or films, to processes for obtaining these articles, and to the cellulose fibres themselves.
The production of viscose and rayon fibres by a wet process has been known for a very long time, in which the formation of the fibre in the coagulation bath is accomplished by coagulation resulting from the dehydrating action of a solution of electrolytes and extraction of the solvent (see "Cellulose Chemistry and its Applications", Ed. T. P. Nevell and S. H. Zeronian, Ellis Horwood Limited, 1985, Chapter 18; and "Physics and Chemistry of Cellulose Fibers" by P. H. Hermans, Elsevier. 1949, Part 3, for example). This process employs a succession of complex steps which have characteristics which are significant as regards pollution.
Various processes have been described aimed at remedying this pollution disadvantage; these are summarised below.
It has been proposed that cellulose be dissolved directly in tertiary amine N-oxides, particularly N-methylmorpholine N-oxide, as described for example in the patents U.S. Pat. No. 4,416,698, U.S. Pat. No. 4,734,239, and DD 298 653. These solvents have the property of decomposing readily, forming peroxides which can lead to explosions and cause degradation of the cellulose. Moreover, the fibres resulting from this process exhibit a marked tendency to fibrillation.
It is known that cellulose fibres can be prepared by dissolving cellulose in a mixture of N,N-dimethylacetamide (DMAC) and LiCl, as described for example in U.S. Pat. No. 4,302,252 and in European Patent Application EP-A-178 293, but this process necessitates prior activation of the cellulose.
Japanese Patent Applications JP-A-60/199 912 and JP-A-60/209 006 describe the production of fibres by employing solutions of cellulose in organic solvents containing halogenated tetraalkylammonium compounds. This process does not permit a concentration of 6% by weight of dissolved cellulose to be exceeded.
Patent Application WO-A-85/05115 and the equivalent patents EP-B-179822 and U.S. Pat. No. 4,839,113 describe the production of cellulose formate fibres from anisotropic solutions of cellulose formate in formic acid and 99% crystalline phosphoric acid, wherein these fibres can be regenerated. The process for obtaining fibres is non-polluting, and the regenerated cellulose fibres thus obtained are characterised by very high mechanical property values; the initial modulus and the tenacity in particular have high values. However, the fibres obtained in this manner have a very ordered structure and a particular morphology which reflect the anisotropic character of the starting solutions, which makes them unsuitable for textile use.
Patent Application WO-A-94/17136 describes regenerated cellulose fibres which are obtained from isotropic solutions of cellulose formate in suitable solvents. The process described in this patent application is non-polluting, and it is very flexible since it enables what are termed "technical" fibres (rayon type) as well as what are termed "textile" fibres (viscose type) to be obtained. The fibres obtained are characterised in particular by a less ordered structure and by a morphology which exhibits greater continuity in the transverse direction compared with the fibres described in WO-A-85105115. However, the values of their elongation at break remain moderate in the majority of cases, which can be troublesome for certain applications, particularly for textile applications.